1. Field of the Invention
The present invention relates to a viscous coupling for vehicles and the like. The coupling utilizes, in action, the viscous resistance of a viscous fluid employed therein to transmit rotary torque.
2. Description of the Prior Art
As is well known, conventional viscous coupling includes the following construction: a first torque-transmitting member; a second torque-transmitting member rotatably arranged relative to the first torque-transmitting member; a working chamber filled with a viscous fluid; a plurality of first plates mounted on the first torque-transmitting member to be non-rotatable relative to the first torque-transmitting member; and a plurality of second plates mounted on the second torque transmitting member to be non-rotatable relative to the second torque-transmitting member, the second plates are interleaved with the first plates in the working chamber.
The viscous resistance of the viscous fluid with respect to the torque-transmitting members to the other torque-transmitting members provides a means to transmit torque between the two torque-transmitting members. The torque automatically varies to be substantially proportional to a difference in rotational speed between the torque-transmitting members.
Further, Japanese Utility Model Laid-Open No. 01-109626 discloses a viscous fluid clutch utilizing the abovementioned conventional viscous coupling. The clutch described in this publication intermittently operates the clutch by the utilization of volume change of a piezoelectric element. The torque is intermittently transmitted between one of the plates and the torque-transmitting member of the viscous coupling.
According to this suggested clutch, one of the plates and the torque-transmitting member are coupled at the time of the expansion of the piezoelectric element and they are uncoupled at the time of its shrinkage. When they are coupled, the viscous fluid slowly flows from contact portions between the plates and piezoelectric element due to the viscosity of the viscous fluid. At the time of shrinkage of the piezoelectric element, the flow of the fluid into the contact portions is slow. For this reason, the response is slow and unsatisfactory in the cases of both coupling and uncoupling of the viscous coupling by the clutch.